Internal combustion engined motor vehicles are conventionally fitted with a starter comprising a drive gear which engages with a ring gear of the engine, for rotationally driving the engine when it is being started.
A starter is generally designed to be used just once for each journey by the vehicle, at the time of starting of the engine.
However, more and more vehicles are fitted with so-called heat engine stop and restart systems, hereinafter designated “heat engine stop-restart system”, otherwise known by the name “stop and start”.
By means of these systems, it is possible to stop the heat engine during the vehicle stoppage phases and to restart it on the occurrence of a stimulus such as the driver's first request or another criterion intended to make fuel savings.
Therefore, in the course of one single journey, the engine is likely to be stopped several times, at each red traffic light or in traffic jams, for example. The starter of a vehicle fitted with a stop-restart system is thus likely to be stressed much more than a starter of a conventional vehicle.
Because of this intensive use, certain parts of the starter are likely to be worn prematurely, thus shortening the starter's life. This is particularly the case with one of the bearings of the starter's armature shaft.
The starter is in fact fitted with an electric motor comprising an armature carried by an armature shaft. An output shaft, coaxial with the armature shaft, is rotationally driven by the latter via an epicyclic gear train speed reducer.
In a known way, an intermediate axial section of the armature shaft carries a planetary gear of the epicyclic gear train speed reducer which transmits rotary movement from the armature shaft to the output shaft. The epicyclic gear train speed reducer comprises an assembly of planetary gears which are carried by the output shaft.
An axial bore is formed in a rear axial end of the speed reducer output shaft. It opens on to the rear radial face of the rear free end of the output shaft and is blind at its other front end.
By means of this configuration, the front free end section of the motor armature shaft can be guided rotationally in the speed reducer output shaft axial bore with the insertion of a plain guide ring or a needle roller guide ring.
However, the armature shaft guiding front end section is of a smaller diameter than the other sections of the armature shaft, particularly to make possible the fitting of elements such as the planetary gear on to the armature shaft but also because the diameter of the bore in the output shaft is limited by the dimensions of the output shaft. The front end guiding section is of a diameter of 10 mm for example.